[SYCL] Remove superfluous C++ linkage spec from assert headers (#15614)

This [PR](#15570) added C++ linkage
specifications for the SYCL wrappers around the STL assert headers
`assert.h` and `cassert`.
For `cassert`, this is actually superfluous since it is purely a C++
header. This PR removes it.

Author: lbushi25

sycl/include/sycl/stl_wrappers/cassert

@@ -16,7 +16,6 @@
 #include <../include/cassert>
 #endif
 
-extern "C++" {
 #ifdef __SYCL_DEVICE_ONLY__
 #include <CL/__spirv/spirv_vars.hpp>
 
@@ -43,4 +42,3 @@ __devicelib_assert_fail(const char *, const char *, int32_t, const char *,
 #endif
 #endif
 #endif
-}

sycl/test/basic_tests/assert_header_with_c_linkage.cpp

@@ -1,18 +1,13 @@
-// RUN: %clangxx -fsycl -DASSERT -fsyntax-only %s
-// RUN: %clangxx -fsycl -DCASSERT -fsyntax-only %s
+// RUN: %clangxx -fsycl -fsyntax-only %s
 
-// Verify that compilation works when assert.h/cassert is wrapped by a C linkage
+// Verify that compilation works when assert.h is wrapped by a C linkage
 // specification.
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#if defined(ASSERT)
 #include <assert.h>
-#elif defined(CASSERT)
-#include <cassert>
-#endif
 
 #ifdef __cplusplus
 }